The present invention relates to tools for tensioning hose clamps or the like, especially for tensioning hose clamps of the type wherein the tightening or tensioning means does not constitute or include screws or analogous threaded components. A clamp which can be tensioned by the tool of the present invention (e.g., to sealingly engage the end of a flexible hose with a nipple which extends into the hose) comprises a strap having two overlapping end portions and defining a loop which surrounds a hose or another workpiece when the clamp is applied. In order to tension the clamp, one end portion of the strap is pulled to reduce the size of the loop while the other end portion is held against movement in response to the application of a pull to the one end portion. The end portions have mating teeth or analogous projections which prevent expansion or enlargement of the loop. Clamps which can be tensioned with the tool of the present invention are disclosed, for example, in commonly owned copending U.S. patent application Ser. No. 258,375 filed Apr. 28, 1981 by Heinz Sauer et al. for "Clamp for hoses or the like" . In the clamp which is disclosed in the U.S. patent application Ser. No. 258,375, the free end or tip of the one end portion of the strap is bent over so as to be engageable by a tool which pulls the one end portion. The other end portion of the strap has an external protuberance against which a portion of the tensioning tool abuts in order to prevent the other end portion from sharing the movement of the one end portion during tensioning of the clamp, i.e., during a reduction of the size of the loop. The tip of the one end portion yields and is bent back into the general plane of the one end portion when the magnitude of the tensioning force reaches a maximum permissible value.
It is already known to employ power tools for the purpose of tightening a hose clamp in the above outlined manner. A known tightening or tensioning tool has a tubular member with an inlet for admission of the one end portion of the strap. The tool further comprises a tensioning element which is installed in the interior of the tubular member and can engage the tip of the inserted one end portion. The tensioning element is movable by the piston rod of a fluid-operated motor to exert a pull on the one end portion of the strap (through the medium of the bentover tip of such end portion). The piston rod can be returned to its normal position (in which the tensioning element is ready to engage the tip of the one end portion of a strap) by a suitable restoring spring. When the tool is in actual use, the tip of the one end portion of the strap is engaged by the tensioning element while the latter is caused to move deeper into the tubular guide whereby the size of the loop is reduced, i.e., the strap is pulled tight around a deformable hose or a like workpiece. The tensioning element urges the one end portion against the inner side of the tubular guide so that it slides along the guide while the size of the loop decreases. This generates a substantial amount of friction between the one end portion of the strap and the internal surface of the guide, and such friction must be overcome by the tool (i.e., the force with which the tensioning element is drawn deeper into the interior of the guide must overcome the resistance of the workpiece to compression, the resistance of the strap to a reduction of the size of its loop as well as the frictional forces which develop between the one end portion of the strap and the tubular guide. This, in turn, entails premature bending of the tip of the one end portion, i.e., the tip yields and is flexed back into the general plane of the one end portion ahead of the time when the dimensions of the loop are reduced to an optimum value. Otherwise stated, friction between the one end portion of the strap and the tubular guide for the tensioning element prevents the bent-over tip of the one end portion from yielding only at such time when the end portion of a hose or a similar workpiece is adequately compressed to prevent leakage of pressurized fluid in an automotive vehicle or elsewhere where hose clamps or analogous devices are used to sealingly connect hoses, pipes, tubes, nipples or analogous workpieces to each other. This, in turn reduces the reliability of connections which are established by resorting to tensioned hose clamps.